Cochlear fenestration burrs

ABSTRACT

Specialized surgical burrs ( 122, 124, 162, 164 ) permit safely fenestrating the otic capsule bone adjacent to the scala tympani ( 44 ) of the cochlea ( 34 ) without damaging the basilar membrane ( 52 ) or organ of cordi. The invention disclosed herein may also be adopted for safely fenestrating other areas of the inner ear such as the scala vestibuli ( 42 ), bony labyrinth of semicircular canals, or walls of the vestibule, or perhaps even the oval or round windows thereof.

TECHNICAL FIELD

The present invention relates to a fully implantable hearing aid system,and more particularly to devices and methods for mounting amicroactuator, or other therapeutic device, into a fenestration thatpierces the wall of the cochlea.

BACKGROUND ART

A biologically sealed attachment into the wall of the cochlea that isstable and watertight is often desired, not only for an acousticactuator, but also for various other medical devices. U.S. Pat. No.5,951,601 (“the '601 patent”) by both of the inventors hereof describesseveral methods for attaching a microactuator to a fenestration throughthe wall of the cochlea.

The invention disclosed in the '601 patent has several advantages. Acasing locates the hearing device very securely, without vibration. Inaddition, the invention makes the removal of the hearing device easy,should this be required. Thirdly, together with an precise atraumaticfenestration procedure it provides for a very precise microactuatorlocation, thereby ensuring that the microactuator is optimally situatedin the cochlea, without damage to the delicate structures of the innerear.

Specifically, the casing disclosed in the '601 patent discloses receivesa microactuator of an implantable hearing aid system. The casing isimplanted into a fenestration that pierces the promontory of the oticcapsule bone. The promontory is a projection of the cochlea which is afluid-filled hearing portion of the inner ear. As described in the '601patent, the casing is adapted for receiving and attaching to the subjecteither a microactuator included in the implantable hearing aid system,or a dummy plug to replace the microactuator should removal of themicroactuator become necessary. Upon application of an electric signalto the microactuator, the microactuator directly stimulates fluid withinthe inner ear, which stimulation the subject perceives as sound.

A casing for attaching a microactuator of an implantable hearing aidsystem to a fenestration formed through a subject's promontory inaccordance with the disclosure of the '601 patent includes a sleeve thathas an outer surface. During implantation of the casing, a first end ofthe sleeve is received into the fenestration. Disposed in that location,the outer surface of the sleeve mates with the fenestration for securingthe casing within the fenestration. The hollow sleeve includes an innersurface adapted to receive a barrel of the microactuator.

The casing also includes a flange that is integral with the sleeve. Theflange projects outward from the outer surface of the sleeve about asecond end of the sleeve that is located distal from the first end. Theflange, through contact either with a mucosa that covers the promontoryor with the promontory itself, limits a depth to which the first end ofthe sleeve may enter into the fenestration.

A casing in accordance with the '601 patent may employ various means forsecuring the sleeve within the fenestration such as screwing into thepromontory or clamping to the promontory. Similarly, such a casing mayfasten the microactuator to the casing in various ways such as by athreaded attachment, with screws, with button-and-socket snap fasteners,or with a slotted tongue-and-groove lock. A casing in accordance withthe '601 patent may also include a keyway that receives a mating keyformed on the barrel of the microactuator for establishing anorientation of the implanted microactuator.

One difficulty in a process for securing a therapeutic appliance intothe wall of the cochlea is that the attachment be biologically sealed.Another difficulty in a process for securing a biologically sealedtherapeutic appliance into the wall of the cochlea is safelyfenestrating the otic capsule bone without damage to the membranouslabyrinth or organ of cordi and thus, without damage to hearing.

DISCLOSURE OF INVENTION

An object of the present invention is to facilitate attachment of amicroactuator of an implantable hearing aid system or other therapeuticappliance, such as a microactuator, plug or micropump for drug ortherapeutic agent delivery, electrodes etc., to a fenestration formedthrough a subject's promontory, and to facilitate the therapeuticappliance's subsequent removal.

Another object of the present invention is to attach a microactuator ofan implantable hearing aid system or other therapeutic appliance, suchas a microactuator, plug or micropump for drug or therapeutic agentdelivery, electrodes etc., to a fenestration formed through the oticcapsule bone of a subject's cochlea.

Another object of the present invention is to provide an easilyimplanted casing for attaching a microactuator of an implantable hearingaid system to a fenestration formed through a subject's promontory.

Yet another object of the present invention is to provide surgical burrsthat permit safely fenestrating the otic capsule bone adjacent to thescala tympani of the cochlea without damage to the membranous labyrinthor organ of cordi and thus, without damage to hearing.

Briefly, one aspect of the present invention relates to securing atherapeutic appliance, such as a microactuator, plug, micropump for drugor therapeutic agent delivery, electrodes, etc., into a fenestrationthat pierces the otic capsule bone of the cochlea. The present inventionincludes several different ways of achieving a “water tight” sealbetween the otic capsule bone and the therapeutic appliance. Theinvention includes specific ways of implanting the therapeutic applianceboth with and without a sheath lining the wall of the fenestration.

Another aspect of the present invention includes specialized surgicalburrs that enable the otologic surgeon to safely fenestrate the oticcapsule bone adjacent to the scala tympani of the cochlea without damageto the basilar membrane or organ of cordi. Utilizing the principles ofthe invention described herein, other areas of the inner ear may besafely fenestrated provided damage to the membranous labyrinth isavoided, e.g., fenestration of the scala vestibuli of cochlea, bonylabyrinth of semicircular canals, or walls of the vestibule. Theinvention disclosed herein might also be adopted for fenestration ofoval or round windows of the inner ear.

These and other features, objects and advantages will be understood orapparent to those of ordinary skill in the art from the followingdetailed description of the preferred embodiment as illustrated in thevarious drawing figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a fenestration that pierces thepromontory of the cochlea having been formed with fenestration burswhich have precise, compound drilling diameters.

FIG. 2 shows a sectioned, prefabricated casing (sleeve) disposed in thefenestration that receives and secures a microactuator.

FIG. 3 shows how the sleeve may be coated on both sides with anelastomeric antibacterial material, thereby providing a very tightcompressive seal.

FIG. 4 shows interposition of an O-ring between the sleeve and themicroactuator.

FIG. 5 illustrates application of sealing rings of silastic or similarbiocompatible material to the sleeve and/or microactuator.

FIG. 6 shows a plug with an expandable bladder for fixation.

FIG. 7 schematically illustrates how the sleeve may be used with a fullyelastomeric plug for delivering a therapeutic agent into the cochlea.

FIG. 8 schematically illustrates how the sleeve may be used with anelastomeric plug and a cochlear electrode implant cable.

FIG. 9 illustrates a elastomeric plug with protruding ring.

FIGS. 10 and 11 schematically illustrate elastomeric plugs inserted intoa fenestration and lacking any sleeve.

FIGS. 12 a and 12 b illustrate fenestration burrs.

FIG. 13 shows a grooveed fenestration for anchoring a microactuator.

FIG. 14 a shows one type of drill that may be used to make a groove intothe wall of the fenestration.

FIG. 14 b shows another type of drill that may be used to make a grooveinto the wall of the fenestration.

FIG. 15 shows the microactuator having protruding elastomeric rings tofit into the groovees.

FIG. 16 is a cross-sectional view of a sleeve illustrating elastomericrings applied thereto to fit into the groovees.

FIG. 17 shows locations for frequency maxima along a basil coil locatedwithin the cochlea, and displacement of the locations for frequencymaxima after treatment of the basilar membrane.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 depicts a promontory wall 32 of a cochlea 34 that, in accordancewith the present invention, is pierced by a fenestration 36. An upperportion of a bony labyrinth within the cochlea 34 is called the scalavestibuli 42, while a lower portion of the bony labyrinth is called thescala tympani 44. A membranous labyrinth within the cochlea 34, calledthe scala media 46, lies between the scala vertibuli 42 and scalatympani 44. A “vestibular membrane,” called Reissner's membrane 48,separates the scala media 46 from the scala vestibuli 42, while abasilar membrane 52 separates the scala media 46 from the scala tympani44. A stria vascularis 54 and spiral ligament 56 are juxtaposed with aninner surface of the promontory wall 32.

FIG. 1 also illustrates how precise location of the fenestration 36 mayadvantageously position a microactuator with great precision in thecochlea 34. Preferably, the cylindrically-shaped fenestration 36includes two precision sections, an outer section 62 having a largerdiameter, and an inner section 64 having a diameter that is smaller thanthat of the outer section 62. The outer section 62 of the fenestration36 may be called a well 66. The fenestration 36 includes ananularly-shaped well floor 68 which spans between one edge of the outersection 62 and one edge of the inner section 64. Configured in this way,the fenestration 36 provides a space such that a microactuator may beintroduced into the scala tympani 44 for stimulating the basilarmembrane 52.

As illustrated in FIG. 2, after the fenestration 36 has been formedthrough the promontory wall 32 a unitary, i.e. one piece, sleeve 72 mayinserted and fixed firmly within the promontory wall 32 of the cochlea34. Generally it is desirable that over time the sleeve 72 attach itselfpermanently to the promontory wall 32. The sleeve 72 may be slit to easeintroduction into the fenestration 36, but it should fit tightly afterbeing inserted. The sleeve 72 is preferably made out of very thintitanium e.g. a few mils thick (1 to 10 mils), although elastomericsleeves may also be used. As described in the '601 patent, the sleeve 72also preferably includes prelocated keyways 74 for receivingcorresponding keys 76 that extend from a microactuator 78. The sleeve 72with its keyways 74 and the keys 76 permit locking the microactuator 78in place by inserting the microactuator 78 into the titanium sleeve 72and rotating it 10° with a very small twist or snap action. Thus, thesleeve 72 precisely locates of the microactuator 78 both laterally andtransversely. In this way the microactuator 78 attaches to the sleeve 72by a method similar to locking a cap on a childproof prescriptionbottle.

Complete hermetic sealing of the sleeve 72 and the microactuator 78 tothe promontory wall 32 is usually accomplished by the body itself. Theendothelial lining of the inner ear and the mucosal lining of the innerear will migrate across a biocompatible membrane, sealing the sleeve 72,microactuator 78 and the fenestration 36, similar to what occurs withthe prosthesis following stapedectomy (i.e. fenestration of the stapes).

To improve on the physical and biological sealing while this processoccurs, as depicted in FIG. 3 a bio-compatible elastomeric coating 82may be applied both on both inside and outside walls of the titaniumsleeve 72. The coatings 82 act as a washer that improves the sealing andfit when the microactuator 78 is inserted into the sleeve 72. Thecoatings 82 may be impregnated with an antibacterial agent, to imbue thesleeve 72 with prophylactic properties.

Alternatively, as depicted in FIG. 4 an O-ring 84 may be interposedbetween a floor wall 86 of the sleeve 72 and a shelf 87 of themicroactuator 78 to provide a totally leak free seal. The coating 82 maystill be applied to the outside of the sleeve 72 to provide a tight sealwith the surrounding promontory wall 32. Similar to the coating 82, theO-ring 84 may likewise be impregnated with a prophylactic compound.

FIG. 5 depicts applying a ring 88 of silastic, Teflon, polyethylene, amaterial which expands upon hydration, or similar biocompatible materialalong the floor wall 86 of the titanium sleeve 72 and/or the shelf 87 ofthe microactuator 78. The rings 88 provide a “water tight” seal betweenthe microactuator 78 and the sleeve 72, and also to act as a “spring” toallow compression and rotation of the microactuator 78 as it is “locked”and thus held in place within the sleeve 72.

Alternatively, a pneumatically or hydraulically expandable bladder 91,surrounding either the sleeve 72 or the microactuator 78 or both, may beused for sealing the microactuator 78 within the promontory wall 32. Asdepicted in FIG. 6, expanding the bladder 91, either pneumatically orhydraulically, tightly seals the microactuator 78 to sleeve 72.

The system described thus far consists of a metal sleeve, accepting ametal body which attaches securely and positively to the former. Thisfenestration 36 and the sleeve 72 secured therein locate themicroactuator 78 precisely in the cochlea 34. Alternatively, it ispossible to replace the metal body of the microactuator 78 with a plugmade from a soft material that fits in the sleeve 72, and which may beheld there by elastic pressure. Under these conditions, the sleeve 72still provides good lateral positioning for the plug, and can also stillprovide good transverse location, such that the plug does not penetratefurther in the cochlea 34 than desired. Such a soft plug may often bedesired when the insert is only temporary, e.g. if the plug is used fordelivering a therapeutic agent into the cochlea 34.

In another application for the titanium sleeve 72, a micropump can besecurely attached to the titanium sleeve 72 in the fenestration 36 todeliver precisely measured doses of medication directly into the innerear. This drug delivery system may be shaped similar to themicroactuator 78, and enclose a therapeutic agent reservoir right atthis location (i.e. for very small volume delivery). The micropump couldcontain the necessary reservoir of medication when only tiny amounts(microliters) will be delivered from a pulsed piezoelectric mechanism atintervals.

If a larger reservoir of medication is required, a hermetically sealedcontainer made from biocompatible materials (e.g., titanium) may beimplanted in the mastoid cavity or subcutaneously. The reservoir isconnected to the implanted micropump by hollow tubing extending from themastoid cavity through the facial recess to a dispensing plug located inthe sleeve 72 at the cochlea 34. The micropump is connected to aprogrammable signal processor and battery implanted either in themastoid cavity or subcutaneously with leads extending through the facialrecess or antrum. The micropump would be activated by telemetry eitherfor single dose or by signal processor programmed by telemetry to adjustthe dosage and frequency of medication delivery to the inner ear. Thesubcutaneous reservoir may be periodically refilled by transcutaneousinjection utilizing sterile techniques.

For example, if the drug reservoir is located away from the inner ear, acapillary connection may be made directly to a plug. In the illustrationof FIG. 7, the titanium sleeve 72 holds a soft elastomeric plug 92 whichreceives one end of a capillary 94. The other end of the capillary 94connects to a reservoir 96 that holds a therapeutic agent. The soft plug92 itself may contain prophylactic agents, for example to guard againstinfection.

FIG. 8 depicts this same approach as applied for introducing a cochlearimplant electrode cable 102 into the cochlea 34. The cochlear implantelectrode cable 102 passes through a hole 104 in the elastomeric plug92. When disposed within the cochlea 34, the cochlear implant electrodecable 102 is free to move until the plug 92 is pressed into place in thesleeve 72. Upon pressing the plug 92 into the sleeve 72, the cochlearimplant electrode cable 102 the hole 104 closes around andcircumferentially clamps the cochlear implant electrode cable 102.Though not illustrated in FIG. 8, the soft plug 92 may be tapered ordouble tapered to provide a good friction fit to the sleeve 72. Hencethe structure schematically illustrated in FIG. 8 provides a leak-tight,bacteria-free seal.

As illustrated in FIG. 9, to provide safe anchoring of the soft plug 92,it may be encircled by a raised ring 112 that is adapted to fit into acorresponding outwardly projecting groove 114 that encircles the sleeve72. Radial compression of the plug 92 upon insertion into the sleeve 72squeezes the hole 104 to thereby fix any object passing therethroughsuch as the capillary 94 or the cochlear implant electrode cable 102which was free to move for adjustment before insertion of the soft plug92. Even a hard plug 92 may also be attached this way to the sleeve 72.

Finally, FIGS. 10 and 11 illustrate that, for some applications, it isalso possible to omit the sleeve 72 altogether; i.e. no sleeve 72 ispresent. Those elements depicted in FIGS. 10 and 11 that are common tothe structures illustrated in FIGS. 1-9 carry the same reference numeraldistinguished by a prime (“′”) designation. In FIG. 10, the compressivebiocompatible elastic plug 92′, used with a remote drug delivery systemhaving a reservoir 96′, is simply squeezed into the fenestration 36′that pierces the promontory wall 32′. FIG. 11 shows a similar plug 92′used with a cochlear implant electrode cable 102′, forced with the plug92′ against the fenestrated promontory wall 32′. As stated previously,the plug 92′ depicted in FIGS. 10 and 11 may contain antibacterialcompounds for prophylactic action. In either instance illustrated byFIGS. 10 and 11, an expanding re-entrant bladder may be used to provideanother way of clamping the plug 92′. Note that the system can again bedesigned such that the compression upon insertion will fix the cochlearimplant electrode cable 102′, which is free to move until the plug 92′is inserted into the promontory wall 32′.

Forming the fenestration 36 into the promontory wall 32 of the cochlea34 or other area of the otic capsule bone as depicted in FIG. 1 issafely performed with guarded fenestration burrs 122 and 124 depictedrespectively in FIGS. 12 a and 12 b. The unitary, i.e. one piece,fenestration burrs 122 and 124 of the present invention permit forming aprecise 1.4 mm diameter inner section 64 of the fenestration 36 and a1.8 mm diameter well 66 in the promontory wall 32 of the cochlea 34 asillustrated in FIG. 1. The fenestration burrs 122 and 124 respectivelyattach to a conventional, low frequency microdrill (

2000 rpm), e.g. Synergy stapes hand piece, for rotating the fenestrationburrs 122 and 124 during formation of the fenestration 36. Since themicrodrill is conventional, it is not illustrated in any of the FIGs. Anelongated shaft 128 of each of the fenestration burrs 122 and 124, withrespect to which all diameters specified below for the fenestrationburrs 122 and 124 are measured, can be readily adapted for use with anyselected one of several commercially available ear microdrills. Thefenestration burrs 122 and 124 are guarded to limit penetration intoscala tympani 44 and thus, avoid injury to the structures of cochlea 34illustrated in FIG. 1.

The initial fenestration burr 122 illustrated in FIG. 12 a hasdimensions that are based on the thickness of the promontory wall 32 atthe proposed fenestration site measured in 12 human cochleae. Theinitial fenestration burr 122 includes a cutting burr 132 that is 1.4 mmin diameter and is located at a distal end of the shaft 128 furthestfrom the microdrill. A second, cylindrically-shaped polishing burr 134is located along the shaft 128 near, e.g. 0.5 mm, from the cutting burr132 and formed concentrically on the shaft 128 with the cutting burr132. The polishing burr 134 is diamond studded, is 1.8 mm in diameterand extends 0.5 mm along the shaft 128 from a washer-shaped flange orcollar 136 that is formed concentrically on the shaft 128 with thecutting burr 132 and the polishing burr 134. During use, the polishingburr 134 drills a 0.5 mm deep well 66, i.e. the outer section 62, in thepromontory wall 32 of the cochlea 34 while the cutting burr 132 beginsforming the smaller diameter inner section 64 of the fenestration 36.The collar 136, which is 2.0 mm in diameter and is juxtaposed with aside of the polishing burr 134 furthest from the cutting burr 132,contacts an outer surface of the promontory wall 32 to limit penetrationof the initial fenestration burr 122 thereinto.

A sequence of five (5) subsequent fenestration polishing burrs 124,illustrated by the fenestration polishing burr 124 in FIG. 12 b, areused to complete penetration of the promontory wall 32 and formation ofthe inner section 64 of the fenestration 36. Each of the fenestrationpolishing burrs 124 includes a polishing burr 142 that is 1.4 mm indiameter. The each of fenestration polishing burrs 124 also includes aprotective washer-shaped collar 146 that is located a short distancefrom the polishing burr 142 as indicated by an arrow 144 in FIG. 12 b,and formed concentrically on the shaft 128 with the polishing burr 142.The distal end of the polishing burrs 142 in the sequence offenestration polishing burrs 124 respectively extend a distance furtherand further from the collar 146. Preferably the distal end of polishingburr 142 in the sequence of fenestration polishing burrs 124 extendsrespectively 0.75 mm, 1.00 mm, 1.25 mm, 1.50 mm and 1.75 mm from thecollar 146. The collar 146 measures 1.8 mm diameter and reaches to awell floor 68 of the well 66, thus centering the polishing burr 142 aswell as limiting it's penetration.

A microactuator, micropump, electrode or similar device may be attachedin the following way to the fenestration 36 in the promontory wall 32 ofthe cochlea 34 or other area of the otic capsule without the sleeve 72lining the fenestration 36. First the fenestration 36 is safely formedin the promontory wall 32 of the cochlea 34 or other area of the oticcapsule using the guarded fenestration burrs 122 and 124 depicted inFIGS. 12 a and 12 b and described above. Next, as depicted in FIG. 13,circumferential grooves 152 and 154 (e.g. 0.10-0.15 mm in depth) aredrilled into the bony wall surrounding the fenestration 36 respectivelyencircling the outer section 62 and the inner section 64 at precisedistances respectively below and above the well floor 68 of the well 66.In certain instances a single groove 152 or 154 may be sufficient forthe intended purpose. The grooves 152 and 154 can be precisely formed asdescribed below using fenestration grooving burrs 162 and 164 depictedrespectively in FIGS. 14 a and 14 b.

Each of the unitary, i.e. one piece, fenestration grooving burrs 162 and164 includes an elongated shaft 166 similar to the shaft 128 of thefenestration burrs 122 and 124 depicted respectively in FIGS. 12 a and12 b. Similar to the fenestration burrs 122 and 124, the fenestrationgrooving burrs 162 and 164 also respectively attach to a conventional,low frequency microdrill (

2000 rpm) that is not illustrated in any of the FIGs. Each of thefenestration grooving burrs 162 and 164 also includes a washer-shapedcollar 168. Each collar 168 is slightly larger than the diameter of theinner section 64 of the fenestration 36 depicted in FIG. 1 (e.g. 1.5 mmdiameter), but smaller than the diameter of the well 66. Such a diameterfor the collar 168 permits resting the collar 168 on the well floor 68of the well 66 when drilling the groove 152 or 154, but allowingmovement of the fenestration grooving burr 162 or 165 laterally,eccentrically 3600 around the circumference of the fenestration duringdrilling.

The fenestration grooving burr 162 depicted in FIG. 14 a also includes acutting wheel 172 that is located at a distal end of the shaft 166 ashort distance from the collar 168 and formed concentrically on theshaft 166 with the collar 168. If the inner section 64 has a diameter of1.4 mm, the well 66 has a diameter of 1.8 mm and the collar 168 has adiameter of 1.4 mm, a 1.4 mm diameter for the cutting wheel 172 permitsdrilling 0.15 mm deep groove 154 circumferentially in the inner section64 of the fenestration 36 at a precise distance below the well floor 68of the well 66. The depth of the groove 154 drilled by the fenestrationgrooving burr 162 is controlled by the difference in diameters betweenthe collar 168 and the cutting wheel 172, and between the inner section64 and the well 66.

The fenestration grooving burr 164 depicted in FIG. 14 b includes thecollar 168 that is located at a distal end of the shaft 166 and acutting wheel 176 that is located along the shaft 166 a short distancefrom collar 168 and formed concentrically on the shaft 166 with thecollar 168. The fenestration grooving burr 164 can be used to make thegroove 152 above the well 66 of the well 66. Again, during formation ofthe groove 152 the collar 168 rests on the well 66 of the well 66. Ifthe well 66 has a diameter of 1.8 mm and the collar 168 a diameter of1.5 mm, a 1.8 mm diameter for the cutting wheel 176, i.e. equal to thediameter of the well 66, produces a 0.15 mm deep groove 152 in thepromontory wall 32 surrounding the well 66 a precise distance above thewell floor 68 of the well 66.

Installation of the microactuator 78, micropump or cochlear implantelectrode cable 102, etc. into the fenestration 36 depicted in FIG. 13can be stabilized in the following way. As depicted in FIG. 15, one ormore rings 182 and 184 of pliable material are permanently attachedaround the microactuator 78 at appropriate locations along themicroactuator 78. Upon inserting the microactuator 78 into thefenestration 36 depicted in FIG. 13, the rings 182 and 184 compress andthen expand into the corresponding grooves 152 and 154 as themicroactuator 78 reaches the proper depth thereby fixing themicroactuator 78 in the grooves 152 and 154. Similar to the ring 88depicted in FIG. 5, several different biocompatible materials may beused for the rings 182 and 184, including silastic, Teflon,polyethylene, a material which expands upon hydration, or similarbiocompatible material. As described above, this method for attachingthe microactuator 78 to the grooved fenestration 36 avoids any need forthe sleeve 72 to line the fenestration 36. Similar to the coating 82depicted in FIG. 3 and the O-ring 84 depicted in FIG. 4, if beneficialthe rings 182 and 184 may be impregnated with prophylactic material.

A ring 186 of pliable biocompatible material may also be applied aroundthe distal end of the microactuator 78 or other device to expand uponreaching the lumen of the cochlea 34, e.g. scala tympani 44 or scalavestibuli 42. Use of the ring 186 may avoid any need for grooving thewall of the fenestration 36, but requires that the fenestration 36 havea precise, pre-established depth.

As best illustrated in FIG. 15, the microactuator 78 includes an outerbarrel 192 which abuts the annularly-shaped shelf 87 along a circularcommon edge 194. During implantation of the microactuator 78 directlyinto the fenestration 36, the outer barrel 192 is inserted into andbecomes fixed firmly in the outer section 62, and the shelf 87 to bejuxtaposed with the well floor 68 of the fenestration 36. Themicroactuator 78 also includes an inner barrel 196 which projects awayfrom the outer barrel 192 and abuts the common edge 194 along a circularcommon edge 198. During implantation of the microactuator 78 directlyinto the fenestration 36, the inner barrel 196 is inserted into andbecomes fixed firmly into the inner section 64.

As depicted in FIG. 16, in those instances in which the sleeve 72 isdesired so the microactuator 78 or other device may be easily removed,the rings 182 and 184 and/or ring 186 are applied abound the sleeve 72rather than the microactuator 78 so the sleeve 72 may be inserted andheld in place within the fenestration 36 similar to the microactuator 78depicted in FIG. 15. As depicted in FIG. 16, a thin layer 202 ofsilastic, Teflon, polyethylene, a material which expands upon hydration,or similar biocompatible material may also be applied to coat the floorwall 86 of the sleeve 72, and/or an optional flange 204 that is locatedat the top of the titanium sleeve 72. The thin layers 202 provide awater tight seal between the microactuator 78 or other device and thesleeve 72, and also act as a spring that allows compression and motionof the microactuator 78 as it is locked and then held in place withinthe sleeve 72. Similar methods may be used for fixing a micropump,electrode, or combination microactuator and electrode in thefenestration 36.

As best illustrated in FIGS. 16 and 2, the sleeve 72 includes an outerwall 212 which abuts the annularly-shaped floor wall 86 along a circularcommon edge 214. During implantation of the sleeve 72 into thefenestration 36, the outer wall 212 is inserted into and becomes fixedfirmly in the outer section 62, and the floor wall 86 becomes juxtaposedwith the well floor 68 of the fenestration 36. The sleeve 72 alsoincludes an inner wall 216 which projects away from the outer wall 212and abuts the common edge 214 along a circular common edge 218. Duringimplantation of the sleeve 72 into the fenestration 36, the inner wall216 is inserted into and becomes fixed firmly into the inner section 64.Implantation of the microactuator 78 into the sleeve 72 causes the outerbarrel 192 to be inserted into and fixed firmly in the outer wall 212,and the shelf 87 to be juxtaposed with the floor wall 86 of the sleeve72. Correspondingly, implantation of the microactuator 78 into thesleeve 72 also causes the inner barrel 196 to be inserted into a fixedfirmly into the inner wall 216.

The most common type of sensorineural hearing loss is decreasedsensitivity to high frequency sound caused by aging, noise exposure,diabetes, oto-toxicity, impaired blood supply to the inner ear, etc.High frequency hearing loss results from a deterioration of hair cellsin a basal coil 222 of the cochlea 34. Because of the complicated natureof haircells, they do not regenerate.

The cochlea 34 acts as a frequency analyzer, with the traveling wavereaching a maximum at various locations along the basilar membrane 52.The high frequency maxima occur in the basal coil 222 of the cochlea 34near the stapes, and the low frequency maxima near the apex due to thestiffness gradient of the basilar membrane 52. This separation of maximaalong the basal coil 222 is schematically illustrated in FIG. 17, whichshows the location of the various frequency maxima along the basilarmembrane 52.

If a therapeutic agent or procedure is introduced into the cochlea 34such that the basilar membrane 52 is made stiffer or its motion in thebasal coil 222 of the cochlea 34 blocked, the traveling wave of basilarmembrane displacement will move towards the apex of the cochlea 34depicted in FIG. 17. For example, the location of maximum displacementfor 10 kHz sound could be moved along the basal coil 222 to the locationthat previously sensed 2 kHz sound, the location of maximum displacementfor 5 kHz might be moved to the area that used to be stimulated by 1 kHzetc.

If the basal coil 222 of scala media 46 has no viable hair cells fromits most proximal point near the round window to the mid turn of thebasal coil 222, then the basal coil 222 would not produce nerve impulsesfor high frequencies, e.g. 10 kHz through 4 kHz, and thus would beinsensitive (

deaf

) to these frequencies. Movement of the traveling wave apically (i.e.towards the apex) along the basilar membrane 52 to a location where haircells are still present would now permit depolarization of those haircells thereby converting the sound into nerve impulses. In this wayintact haircells are all used to the maximum extent possible to coverthe entire frequency range.

Computer simulation studies and mechanical models of the cochlea 34indicate that if the traveling wave is moved apically the wave envelopeis compressed but still the

phase/time

analysis performed by the traveling wave is maintained in thiscompressed state. Clinical studies from electrical stimulation of thecochlea 34 with cochlear implants confirm that the brain can beretrained to interpret these new auditory messages, and speechdiscrimination is possible. In essence, by moving the traveling waveapically in a subject who has no surviving hair cells in the basal coil222 permits stimulating the remaining hair cells with high frequenciesthereby allowing them to

volley

in synchrony with the high frequencies. Neuro-physiologic studiesconfirm that hair cells throughout the cochlea 34 have similardepolarization/repolarization characteristics and thus theoretically arecapable of synchronous depolarization at frequencies from 100 to 20 kHzthroughout the cochlea 34.

Hearing sensitivity of the cochlea 34 is measured by pure tone thresholdbone conduction audiometric studies, which stimulate the fluid withinthe cochlea 34 directly. High frequency nerve loss implies a loss ofhair cells in the basal coil 222 of the cochlea 34. Because the locationof frequency maxima along the basilar membrane 52 is well known, theamount of transposition of the traveling wave to areas where hair cellsare intact can be determined by bone conduction audiometry. Thetreatment of the basilar membrane 52 would then be adapted so that therequired basilar membrane stiffening or restriction of its motion iseffected to that degree required for correctly projecting sound atspecific frequencies onto the remaining part of the basal membrane whichhas intact hair cells.

Stiffening the basilar membrane 52 could be accomplished with atherapeutic agent such as a drug, a cell regrowth factor, or any factorthat reduces or stiffens the elasticity of the basilar membrane 52. Analternative method is to obstruct the motion of the basilar membrane 52in the scala tympani 44 by physically limiting its downward motion witha bio-compatible material which would completely obstruct scala tympani44 in the basal coil 222 to the desired length of the cochlea 34. Thiswould require creating a new round window in the scala tympani distal tothe point of obstruction if sound vibrations are to enter the cochlea 34through the oval window. Conversely, a microactuator could be attachedto the distal end of the material obstructing the scala tympani 44, andsound introduced directly into scala tympani 44. In this scenario, theoval window would provide the necessary hydraulic decompression topermit the traveling wave of pressure and displacement withoutsignificantly increasing fluid impedance. It is recognized because ofthe impedance mismatching of the basilar membrane 52 that greater energywill be necessary to displace the basilar membrane 52 with thisobstructing technique. Again the traveling wave envelope will becompressed in both the horizontal and vertical planes.

INDUSTRIAL APPLICABILITY

In general, many if not all of the methods depicted in FIGS. 3 through11 and described above can be used when attaching a microactuator, amicropump, capillary, electrode, or combination microactuator/electrodeinto a fenestration 36 that pierces the wall of the cochlea 34.

Using structures such as those depicted in FIGS. 7 and 10, it isanticipated that conditions such as vertigo, tinnitus, suddensensorineural hearing loss, endolymphatic hydrops (Ménière's disease),autoimmune inner ear disease, and serous or viral labyrinthitis could beimproved by delivering carefully measured doses of a variety ofmedications (steroids, vasodilators, immune suppressants,anticoagulants, antibiotics, antiviral agents, plasma expanders,antioxidants, etc.) directly into the inner ear. Research has recentlydiscovered that hair cells in the cochlea 34 and vestibular labyrinth ofsome vertebrates have the ability to regenerate. Perhaps one day it maybe possible to deliver a substance (e.g., neurohormone, hair cell DNAactuator) into the inner ear that will stimulate the regrowth of haircells in the cochlea 34 in patients with sensorineural hearing loss orrepair damaged vestibular hair cells.

Another use for this invention depicted in FIGS. 8 and 11 is introducingan electrode into the inner ear and securely attaching it to the bonywalls of the promontory wall 32. In addition to fixing the cochlearimplant electrode cable 102 into the cochlea 34, application of low doseelectrical current can depolarize hair cells or neurons and may somedaybe used to relieve tinnitus or vertigo triggered by irritable peripheralhair cells or afferent neurons.

In each of the applications described above, attaching themicroactuator, micropump, or electrode to the titanium sleeve 72 liningthe fenestration 36 enables the surgeon to remove the device withminimal risk of damage to the inner ear. A new device can be inserted toreplace an existing one, or an existing device may replaced by a “plug”if the device is no longer needed.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is purely illustrative and is not to be interpreted aslimiting. Consequently, without departing from the spirit and scope ofthe invention, various alterations, modifications, and/or alternativeapplications of the invention will, no doubt, be suggested to thoseskilled in the art after having read the preceding disclosure.Accordingly, it is intended that the following claims be interpreted asencompassing all alterations, modifications, or alternative applicationsas fall within the true spirit and scope of the invention.

1: A unitary initial fenestration burr adapted for use for conjunctionwith a microdrill in forming a cylindrically-shaped fenestration througha wall of a cochlea of a subject, the fenestration including an outersection that is called a well and an inner section which is smaller indiameter than the outer section, the fenestration also including anannularly-shaped well floor that spans between one edge of the outersection of the fenestration and one edge of the inner section thereof,the initial fenestration burr comprising: an elongated shaft one end ofwhich is adapted to be secured to the microdrill for rotating theinitial fenestration burr during use thereof in forming thefenestration; a cutting burr that is located at a distal end of saidshaft furthest from the microdrill during use of the initialfenestration burr in forming the fenestration; a cylindrically-shapedouter section polishing burr that is located along said shaft near saidcutting burr and which, during use of the initial fenestration burr informing the fenestration, forms the outer section thereof, said outersection polishing burr having a diameter that is larger in a directionorthogonal to said shaft than a diameter of said cutting burr in adirection orthogonal to said shaft; and a washer-shaped initial burrcollar that is: a) larger in diameter in a direction orthogonal to saidshaft than a diameter of said outer section polishing burr in adirection orthogonal to said shaft; b) located along said shaftjuxtaposed with a side of said outer section polishing burr that isfurthest from said cutting burr; and c) adapted to contact an outersurface of the wall of the cochlea during use of the initialfenestration burr in forming the fenestration to thereby limitpenetration of the initial fenestration burr into the wall of thecochlea. 2: The initial fenestration burr of claim 1 wherein saidcutting burr has a diameter in a direction orthogonal to said shaft thatdoes not exceed 1.4 mm. 3: The initial fenestration burr of claim 1wherein said outer section polishing burr has a diameter in a directionorthogonal to said shaft that does not exceed 1.8 mm. 4: The initialfenestration burr of claim 1 wherein said outer section polishing burris located 0.5 mm from said cutting burr along said shaft. 5: Theinitial fenestration burr of claim 1 wherein said outer sectionpolishing burr is located 0.5 mm from said cutting burr along said shaftand extends 0.5 mm along said shaft. 6: The initial fenestration burr ofclaim 1 wherein said outer section polishing burr is diamond studded. 7:The initial fenestration burr of claim 1 wherein said initial burrcollar has a diameter in a direction orthogonal to said shaft that doesnot exceed 2.0 mm. 8: The initial fenestration burr of claim 1 wherein:said cutting burr has a diameter in a direction orthogonal to said shaftthat does not exceed 1.4 mm; said outer section polishing burr: has adiameter in a direction orthogonal to said shaft that does not exceed1.8 mm; is located 0.5 mm from said cutting burr along said shaft;extends 0.5 mm along said shaft; and is diamond studded; and saidinitial burr collar has a diameter in a direction orthogonal to saidshaft that does not exceed 2.0 mm. 9: A unitary fenestration polishingburr adapted for use in conjunction with a microdrill in forming acylindrically-shaped fenestration through a wall of a cochlea of asubject, the fenestration including an outer section that is called awell and an inner section which is smaller in diameter than the outersection, the fenestration also including an annularly-shaped well floorthat spans between one edge of the outer section of the fenestration andone edge of the inner section thereof, the fenestration polishing burrcomprising: an elongated shaft one end of which is adapted to be securedto the microdrill for rotating the fenestration polishing burr duringuse thereof in forming the fenestration; an inner section polishing burrthat is located at a distal end of said shaft furthest from themicrodrill during use of the fenestration polishing burr in forming thefenestration; and a washer-shaped polishing burr collar that: a) has adiameter in a direction orthogonal to said shaft which: i. is largerthan a diameter of said inner section polishing burr in a directionorthogonal to said shaft; and ii. does not exceed a diameter of saidouter section of the fenestration in a direction orthogonal to saidshaft; b) is located along said shaft a short distance from said innersection polishing burr; and c) is adapted to contact the well floor ofthe well during use of the inner section polishing burr in forming thefenestration to thereby limit penetration of said fenestration polishingburr into the wall of the cochlea. 10: The fenestration polishing burrof claim 9 wherein the diameter of said polishing burr collar in adirection orthogonal to said shaft is the same as the diameter of theouter section of the fenestration in a direction orthogonal to saidshaft. 11: The fenestration polishing burr of claim 9 wherein thediameter of said polishing burr collar in a direction orthogonal to saidshaft does not exceed 1.8 mm. 12: A unitary outer-section grooving burradapted for use in conjunction with a microdrill for forming an outerfenestration section groove that encircles an outer section, that iscalled a well, of a cylindrically-shaped fenestration that pierces awall of a cochlea of a subject; the fenestration further including aninner section which is smaller in diameter than the outer sectionthereof, the fenestration also including an annularly-shaped well floorthat spans between one edge of the outer section of the fenestration andone edge of the inner section thereof, the outer-section grooving burrcomprising: a) an elongated outer section grooving shaft one end ofwhich is adapted to be secured to the microdrill for rotating theouter-section grooving burr during use thereof for forming the outerfenestration section groove; b) a washer-shaped outer fenestrationgroove collar that is located at a distal end of said shaft furthestfrom the microdrill for contacting the well floor during use of theouter-section grooving burr for forming the outer fenestration sectiongroove to thereby locate the outer fenestration section groove at aprecise distance above the well floor, the outer fenestration groovecollar having a diameter that is; i. larger than a diameter of saidinner section; and ii. smaller than a diameter of said outer section;and c) an outer section groove cutting wheel that: i. has a diameter ina direction orthogonal to said shaft which: 1) is larger than a diameterof said outer fenestration groove collar in a direction orthogonal tosaid shaft; and 2) does not exceed a diameter of said outer section ofthe fenestration in a direction orthogonal to said shaft; and ii. islocated along said outer section grooving shaft a short distance fromsaid outer fenestration groove collar. 13: The outer-section groovingburr of claim 12 wherein the diameter of said outer section groovecutting wheel does not exceed 1.8 mm. 14: A unitary inner-sectiongrooving burr adapted for use in conjunction with a microdrill forforming an inner fenestration section groove that encircles an innersection of a cylindrically-shaped fenestration that pierces a wall of acochlea of a subject; the fenestration further including an outersection, that is called a well, which is larger in diameter than theinner section thereof, the fenestration also including anannularly-shaped well floor that spans between one edge of the outersection of the fenestration and one edge of the inner section thereof,the inner-section grooving burr comprising: a) an elongated innersection grooving shaft one end of which is adapted to be secured to themicrodrill for rotating the inner-section grooving burr during usethereof for forming the inner fenestration section groove; b) an innersection groove cutting wheel that: i. has a diameter in a directionorthogonal to said shaft which does not exceed a diameter of the innersection of said fenestration; and ii. is located at a distal end of saidshaft furthest from the microdrill; and c) a washer-shaped innerfenestration groove collar: i. having a diameter that is: 1) larger thana diameter of said inner section; and 2) smaller than a diameter of saidouter section; and ii. that is located along said inner section groovingshaft a short distance from said inner section groove cutting wheel forcontacting the well floor during use of the inner-section grooving burrfor forming the inner fenestration section groove to thereby locate theinner fenestration section groove at a precise distance below the wellfloor. 15: The inner-section grooving burr of claim 14 wherein thediameter of said inner section groove cutting wheel does not exceed 1.4mm. 16: A sequence of unitary fenestration polishing burrs adapted foruse in conjunction with a microdrill in forming a cylindrically-shapedfenestration through a wall of a cochlea of a subject, the fenestrationincluding an outer section that is called a well and an inner sectionwhich is smaller in diameter than the outer section, the fenestrationalso including an annularly-shaped well floor that spans between oneedge of the outer section of the fenestration and one edge of the innersection thereof, each of the fenestration polishing burrs in thesequence comprising: an elongated shaft one end of which is adapted tobe secured to the microdrill for rotating the fenestration polishingburr during use thereof in forming the fenestration; an inner sectionpolishing burr that is located at a distal end of said shaft furthestfrom the microdrill during use of the fenestration polishing burr informing the fenestration; and a washer-shaped polishing burr collarthat: a) has a diameter in a direction orthogonal to said shaft which:i. is larger than a diameter of said inner section polishing burr in adirection orthogonal to said shaft; and ii. does not exceed a diameterof said outer section of the fenestration in a direction orthogonal tosaid shaft; b) is located along said shaft a short distance from saidinner section polishing burr; and c) is adapted to contact the wellfloor of the well during use of the inner section polishing burr informing the fenestration to thereby limit penetration of saidfenestration polishing burr into the wall of the cochlea; and thedistance between said polishing burr collar and a distal end of saidinner section polishing burr increasing progressively for eachsuccessive fenestration polishing burr in the sequence of fenestrationpolishing burrs. 17: The sequence of fenestration polishing burrs ofclaim 16 wherein the diameter of said polishing burr collar in adirection orthogonal to said shaft for each successive fenestrationpolishing burr in the sequence of fenestration polishing burrs is thesame as the diameter of the outer section of the fenestration in adirection orthogonal to said shaft. 18: The sequence of fenestrationpolishing burrs of claim 16 wherein the diameter of said polishing burrcollar in a direction orthogonal to said shaft for each successivefenestration polishing burr in the sequence of fenestration polishingburrs does not exceed 1.8 mm. 19: The sequence of fenestration polishingburrs of claim 16 wherein: there are five (5) fenestration polishingburr in the sequence of fenestration polishing burrs; a shortestdistance between said polishing burr collar and a distal end of saidinner section polishing burr of one of the fenestration polishing burrsis 0.75 mm; and the distance between said polishing burr collar and adistal end of said inner section polishing burr for other fenestrationpolishing burrs in the sequence of fenestration polishing burrsprogressively increases: from 0.75 mm to 1.00 mm; from 1.00 mm to 1.25mm; from 1.25 mm to 1.50 mm; and from 1.50 mm to 1.75 mm. 20: A set offenestration burrs adapted for use in conjunction with a microdrill informing a cylindrically-shaped fenestration through a wall of a cochleaof a subject, the fenestration including an outer section that is calleda well and an inner section which is smaller in diameter than the outersection, the fenestration also including an annularly-shaped well floorthat spans between one edge of the outer section of the fenestration andone edge of the inner section thereof, the initial fenestration burrcomprising: a) a unitary initial fenestration burr that includes: i. anelongated initial burr shaft one end of which is adapted to be securedto the microdrill for rotating the initial fenestration burr during usethereof in forming the fenestration; ii. a cutting burr that is locatedat a distal end of said initial burr shaft furthest from the microdrillduring use of the initial fenestration burr in forming the fenestration;iii. a cylindrically-shaped outer section polishing burr that is locatedalong said initial burr shaft near said cutting burr and which, duringuse of the initial fenestration burr in forming the fenestration, formsthe outer section thereof, said outer section polishing burr having adiameter that is larger in a direction orthogonal to said initial burrshaft than a diameter of said cutting burr in a direction orthogonal tosaid initial burr shaft; and iv. a washer-shaped initial burr collarthat is: 1) larger in diameter in a direction orthogonal to said initialburr shaft than a diameter of said outer section polishing burr in adirection orthogonal to said initial burr shaft; 2) located along saidinitial burr shaft juxtaposed with a side of said outer sectionpolishing burr that is furthest from said cutting burr; and 3) adaptedto contact an outer surface of the wall of the cochlea during use of theinitial fenestration burr in forming the fenestration to thereby limitpenetration of the initial fenestration burr into the wall of thecochlea; and b) a sequence of unitary fenestration polishing burrs, eachof the fenestration polishing burrs in the sequence including: i. anelongated polishing burr shaft one end of which is adapted to be securedto the microdrill for rotating the fenestration polishing burr duringuse thereof in forming the fenestration; ii. an inner section polishingburr that is located at a distal end of said polishing burr shaftfurthest from the microdrill during use of the fenestration polishingburr in forming the fenestration; and iii. a washer-shaped polishingburr collar that: 1) has a diameter in a direction orthogonal to saidpolishing burr shaft which: A. is larger than a diameter of said innersection polishing burr in a direction orthogonal to said polishing burrshaft; and B. does not exceed a diameter of said outer section of thefenestration in a direction orthogonal to said polishing burr shaft; 2)is located along said polishing burr shaft a short distance from saidinner section polishing burr; and 3) is adapted to contact the wellfloor of the well during use of the inner section polishing burr informing the fenestration to thereby limit penetration of saidfenestration polishing burr into the wall of the cochlea; and thedistance between said polishing burr collar and a distal end of saidinner section polishing burr increasing 70 progressively for eachsuccessive fenestration polishing burr in the sequence of fenestrationpolishing burrs. 21: The set of fenestration burrs of claim 20 whereinsaid cutting burr of said initial fenestration burr has a diameter in adirection orthogonal to said shaft that does not exceed 1.4 mm. 22: Theset of fenestration burrs of claim 20 wherein said outer sectionpolishing burr of said initial fenestration burr has a diameter in adirection orthogonal to said shaft that does not exceed 1.8 mm. 23: Theset of fenestration burrs of claim 20 wherein said outer sectionpolishing burr of said initial fenestration burr is located 0.5 mm fromsaid cutting burr along said shaft. 24: The set of fenestration burrs ofclaim 20 wherein said outer section polishing burr of said initialfenestration burr is located 0.5 mm from said cutting burr along saidshaft and extends 0.5 mm along said shaft. 25: The set of fenestrationburrs of claim 20 wherein said outer section polishing burr of saidinitial fenestration burr is diamond studded. 26: The set offenestration burrs of claim 20 wherein said initial burr collar of saidinitial fenestration burr has a diameter in a direction orthogonal tosaid shaft that does not exceed 2.0 mm. 27: The set of fenestrationburrs of claim 20 wherein: said cutting burr of said initialfenestration burr has a diameter in a direction orthogonal to said shaftthat does not exceed 1.4 mm; said outer section polishing burr of saidinitial fenestration burr: has a diameter in a direction orthogonal tosaid shaft that does not exceed 1.8 mm; is located 0.5 mm from saidcutting burr along said shaft; extends 0.5 mm along said shaft; and isdiamond studded; and said initial burr collar of said initialfenestration burr has a diameter in a direction orthogonal to said shaftthat does not exceed 2.0 mm. 28: The set of fenestration burrs of claim20 wherein the diameter of said polishing burr collar of eachfenestration polishing burr in the sequence of fenestration polishingburrs in a direction orthogonal to said shaft is the same as thediameter of the outer section of the fenestration in a directionorthogonal to said shaft. 29: The set of fenestration burrs of claim 20wherein the diameter of said polishing burr collar of each fenestrationpolishing burr in the sequence of fenestration polishing burrs in adirection orthogonal to said shaft does not exceed 1.8 mm. 30: Thesequence of fenestration polishing burrs of claim 20 wherein: there arefive (5) fenestration polishing burr in the sequence of fenestrationpolishing burrs; a shortest distance between said polishing burr collarand a distal end of said inner section polishing burr of one of thefenestration polishing burrs is 0.75 mm; and the distance between saidpolishing burr collar and a distal end of said inner section polishingburr for other fenestration polishing burrs in the sequence offenestration polishing burrs progressively increases: from 0.75 mm to1.00 mm; from 1.00 mm to 1.25 mm; from 1.25 mm to 1.50 mm; and from 1.50mm to 1.75 mm. 31: The set of fenestration burrs of claim 20 furthercomprising a unitary outer-section grooving burr adapted for use inconjunction with a microdrill for forming an outer fenestration sectiongroove that encircles the outer section of the fenestration, theouter-section grooving burr comprising: a) an elongated outer sectiongrooving shaft one end of which is adapted to be secured to themicrodrill for rotating the outer-section grooving burr during usethereof for forming the outer fenestration section groove; b) awasher-shaped outer fenestration groove collar that is located at adistal end of said shaft furthest from the microdrill for contacting thewell floor during use of the outer-section grooving burr for forming theouter fenestration section groove to thereby locate the outerfenestration section groove at a precise distance above the well floor,the outer fenestration groove collar having a diameter that is; i.larger than a diameter of said inner section; and ii. smaller than adiameter of said outer section; and c) an outer section groove cuttingwheel that: i. has a diameter in a direction orthogonal to said shaftwhich: 1) is larger than a diameter of said outer fenestration groovecollar in a direction orthogonal to said shaft; and 2) does not exceed adiameter of said outer section of the fenestration in a directionorthogonal to said shaft; and ii. is located along said outer sectiongrooving shaft a short distance from said outer fenestration groovecollar. 32: The outer-section grooving burr of claim 31 wherein thediameter of said outer section groove cutting wheel does not exceed 1.8mm. 33: The set of fenestration burrs of claim 20 further comprising aunitary inner-section grooving burr adapted for use in conjunction witha microdrill for forming an inner fenestration section groove thatencircles the inner section of the fenestration that pierces thecochlea, the inner-section grooving burr comprising: a) an elongatedinner section grooving shaft one end of which is adapted to be securedto the microdrill for rotating the inner-section grooving burr duringuse thereof for forming the inner fenestration section groove; b) aninner section groove cutting wheel that: i. has a diameter in adirection orthogonal to said shaft which does not exceed a diameter ofthe inner section of said fenestration; and ii. is located at a distalend of said shaft furthest from the microdrill; and c) a washer-shapedinner fenestration groove collar: i. having a diameter that is: 1)larger than a diameter of said inner section; and 2) smaller than adiameter of said outer section; and ii. that is located along said innersection grooving shaft a short distance from said inner section groovecutting wheel for contacting the well floor during use of theinner-section grooving burr for forming the inner fenestration sectiongroove to thereby locate the inner fenestration section groove at aprecise distance below the well floor. 34-49. (canceled)